Condition responsive switch apparatus



May 14, 1957 R. P. SWEGER 2,792,475

CONDITION RESPONSIVE SWITCH APPARATUS Filed Oct. 21, 1954 2 Sheets-Sheetl INVENTOR. fiusse?! fijn gger Cit/1m ATTORNEYS May 14, 1957 R. P.SWEGER 2,792,475

CONDITION RESPONSIVE SWITCH APPARATUS Filed Oct. 21, 1954 2 Sheets-Sheet2 L 2o I IN V EN TOR.

[Passe]? Swqger BY a t 3 (Law/(M 42 ATTURNE Y5 United States Patent Thisinvention relates to a switch responsive to a change in condition suchas temperature and, more particularly, to a snap act-ion switch in whicha movable contact is supported by an over-center spring.

in a switch of this type, a lesser force is' required to hold the springin the over-center position than is needed to snap the spring HCEOSScenter.

The general object of the invention is to provide a new and improvedapparatus of the above character in which the switch operates in onedirection at a predetermined valueofthe condition as the latterincreases and at a diflerent'value as the condition decreases and inwhich -the differential between the two operating values is maintainedprecisely.

A more detailed object is to obtain the diiferential by taking advantageof the difierent forces required to move and to hold the switch throughthe use t a two-way lost motion connectionv formed by a switch actuatingelement moving between spac d abutments and supported by a second springwhich exerts a force of a magnitude between the forces of the switchspring so that the element may yield without actuating the switch until.engaged by one or the other of the abutments.

Another object is to support the actuating element on a lever which isrocked about its fulcrum in response to changes in the condition beingsensed and to adjust the position of the fulcrum to vary the magnitudesof the condition at which the switch is actuated.

A.- further object is to utilize the movable fulcrum in providing ameans which permits the lever to move beyond its normal range withoutdamaging connected or adjacent parts.

The invention also resides in the novel construction and arrangement ofthe various parts of the apparatus and especially of the actuatingelement, abutments, lever and fulcrum.

Other objects and advantages of the invention will become apparent fromthe following detailed description taken in connection with theaccompanying drawings, in which Figure l isa front view of thermostatembodying the novel features of the present invention, parts beingbroken away. and shown in section.

Fig. 2 is a sectional view taken along the line 22 in Fig. 1.

Fig. 3 is a sectional view taken along the line 3--3 in Fig. l.

Fig. 4 is a perspective view of the lever supporting the actuatingelement.

'Fig. 5 is a fragmentary vertical sectional view of the lever and theswitch with the latter shown schematically.

The invention is directed to a switch apparatus responsive to changes ina condition and, as shown in the drawings for purposes of illustration,is particularly adapted for use in a thermostat. For this purpose, themovable contact of aswitch 11 is moved back and forth from onestationary contact 12 to another contact 13 in response to'the movementof a resilient metallic bellows pin and acts between the head 34 of thepin 2,792,475 Patented May 14, 1957 l t-which is connected through atube 15 to a remote temperature sensitive bulb 16. Thus, changes in thetemperature surrounding the bulb expands or contracts the bellows andthis is transmitted to the switch 11 through a movable member 17. Thelatter preferably is a lever formed from a sheet metal strip withdownturned side flanges 18 and is fuicrumed at one end on a pin 1;projecting through the flanges. At its other end, the lever carries anactuating element 20 which engages anddepresses the actuator 21 of theswitch.

Enclosing the switch 11 and the. lever 17 is a casing 22 composed of aflanged mounting plate 23 and an L-shaped cover 24 (Fig. 2). The switchis disposed within a housing .25 of insulating material and the contactslull; and 13 are connected to terminals 26 which, in turn, are connectedby rigid right angle leads 27 to the terminalsZS of a terminal plate 29.The latter is disposed against the side of the housing 25 and is held inplace by the ieads 27, the housing and the plate being; secured tothemounting plate by screws The .beilows i4 is su ported within a on thelower flange "*2 of the plate 2-3 by a cap 2 -3 bo'ted the boss.

Projecting siidably into the boss 31 and abutting against upper end ofbellows i l is the head 34 of a vertical .pin 35. At its upper end, thepin bears against the lower pointed end of a screw 36 threaded throughthe lever 17. Acoiled compression spring 37 encircies the astationaryccllar 38 encirclin the pin and rigid with the plate 23 sothat the spring opposes the resiliency or" the bellows l4 and loads thelatter. A contractile spring 3; is anchored at one end to a lug 49 onthe bottom flange 32 and at the other end to an car 41 struck down fromthe lever 17 between the fulcrum pin 19 and the screw 36. The spring 39thus biases the lever toward the pin 35 and the lever swings back andforth about its fulcrum upon expansion and contraction of the bellows 14and hence in response to temperature changes.

In the present instance, the switch 11 is of the snap action type, suchas those commonly-sold under the trade name Micro Switch," and, for thispurpose, the movable contact 10 is supported on one end of a cantileverspring 42. At the other end, the spring is secured to thehousinga25cand, between its ends, the spring is engaged by the. innerendof the actuator 21 which is a pin projecting through the housing. Thespring 42 normally holds the movable contact 10 against the contacti2but, when the actuator 21 is depressed, the spring moves over center andsnaps the movable Contact across to the contact 13.

In a switch of the above type, a greater force is required to move thespring 42 across center than is needed to .hold the. spring in theover-center position. For ex ample, :a force as high as 11 ounces may berequired to snap the movable contact 10 over against the contact 13while a force of 7 ounces will hold the movable contact in thisposition. According to the present invention, advantage is taken of thisdiiference in forces to obtain a differential in magnitudes of thecondition at which the apparatus responds as the condition changes inopposite directions. Thus, in the thermostat shown, the contact 10 movesover center at a predetermined temperature upon afall in temperature butdoes not move back upon a rise until'a higher temperature is reached.

To obtain the differential in the temperatures at which the switchlloperates, the actuating element 20 is part of a two-Way lost motionconnection and is resiliently mounted on the lever 17 by means of aspring 43 which exerts a force less than that required to move theswitch spring 42 across center but sufficient to hold the spring in theover-center position. In the illustration given above, for example, thespring'43 might exert a force of 9 ounces. By virtue of this mounting,the'spring'43 urges 3 the actuating element 20 down against the actuator21 but the element yields as the lever 17 swings down. Movement of theelement relative to the lever is limited in the downward direction by anabutment 44 (Fig. 5) and in the opposite direction by an abutment 45,both abutments being rigid with the lever. 7

With the foregoingarrangement, a temperature drop contacts the bellows14 which, through medium of the pin 35, permits the lever 17 to swingdown under the action of the spring 39, the latter being stronger thaneither of the springs 42 and 43. During this turning of the lever, theelement 20 engages the actuator 21 and, since the spring 43 is weakerthan the switch spring, it yields until engaged by the abutment 45.Thereupon, further downward swinging of the lever depresses the actuator21 snapping the switch spring 42 across center and moving the contactagainst the contact 13. With a rise in temperature, the bellows expandsturning the lever back up. Because the spring 43 now is stronger thanthe switch spring 42, the element holds the actuator pin 21 depressed.As a result, the elements remain stationary during upward swinging ofthe lever until it is picked up by the abutment 44 and raised away fromthe actuator pin permitting the switch spring 42 to snap the contact 10back against the contact 12. Thus a higher temperature is required torelease the switch actuator than has been needed to depress it.

Herein, the actuating element 20 and the spring 43 are formed integrallyas an elongated fiat leaf spring with one end 46 (Fig. 5) inserted in aslot 47 in the lever 17 near the screw 36 and hooked over a lug 48 toanchor this end to the lever. From the anchored end 46, the springprojects down from the lever, through a slot 49 in an ear 5! struck downfrom the lever and then is flexed to extend generally parallel to thelever. The free end of the leaf spring projects through a hole 51 inanother ear 52 struck down from the lever near the outer end thereof andconstitutes the actuating element 20. The

hole 51 is comparatively wide in the vertical dimension to permit thespring end 29 to flex up away from the lower edge of the hole which edgethus forms the abutment 44. The upper abutment 45 is formed by a screw53 threaded through the outer end of the lever. By threading this screwin or out the amount the end 20 may flex relative to the lever may bevaried thus setting the difierential between the operating values of theswitch 11.

In order to adjust the control point of the apparatus, that is, theposition of the operating differential on the temperature scale, thefulcrum pin 19 is arranged to be moved up and down to raise or lower thetemperature value at which the switch 11 is actuated. For this purpose,the pin 19 is fixed to and extends ttransversely through the lower endof a vertical rod 54 which slides up and down through a circular boss 55upstanding from the upper flange 56 of the support plate 23. The rod isguided additionally in its vertical movement by the pin 19 whose endsare received in elongated vertical parallel guideways 57 and 58, theformer being a recess in a boss 59 (Fig. 2) on the plate 23 while thelatter is a slot in a small plate 60 bolted to the boss.

Threaded on the end of the rod 54 beyond the boss 55 is a knob 61 whichis formed with a depending annular flange 62 to provide an internalshoulder 63. The latter abuts against the upper end of the boss 55 andis held in this position by the spring 39. By threading the knob 61 upand down on the rod 54, the vertical position of the fulcrum pin 19 isvaried. This changesthe amount of expansion or contraction of thebellows 14 required to actuate the switch thereby adjusting the controlpoint of the apparatus. The knob 61 may be marked with indiciacooperating wim a mark on the flange 56 to indicate the adjustedposition of the fulcrum.

The foregoing arrangement of the fulcrum pin 19 may also be utilized tolimit the amount of upward movement I of the outer end of the lever 17in the event of abnormal conditions without damage to any of the partsso as to protect any other equipment which may be located above thisend. T 0 this end, a limit stop 64 rigid with the support plate 23 isdisposed above the lever 17 between the screw 36 and the free end of thelever. When temperatures substantially exceeding the normal range areencountered, the lever engages the stop 64 and further expansion of thebellows 14 causes the lever to fulcrum about the stop. This raises theshoulder 63 ofi the boss 55 lifting the pivot pin 19 against the actionof the spring 39 without raising the outer end of the lever.

It will be observed that an apparatus constructed in accordance with theinvention produces an accurate differential between the temperature atwhich the switch operates upon a temperature rise and the value at whichit operates on a fall. This is maintained precisely because, in eachdirection of temperature change, the actuating element 20 is moved bythe positive action of one or the other of the abutments 44 and 45. Inaddition, the movable fulcrum pin 19 provides a simple but effectivemeans for adjusting the control point of the switch and, at the sametime, is adapted for use in preventing over-travel of the outer end ofthe lever 17. By using a separate spring 37 to load the bellows 14, thespring 39 biasing the lever against the bellows pin 35 need only besufficient to overcome the elfects of the springs 42 and 43. Thus, thespring 39 may be comparatively weak so as to prevent the pivot pin 19from being subjected to excessive pressure. Further, the spring 39 isconnected to the lever near the operating point of the bellows, that is,near the screw 36 and, as a result, the force of this spring is notincreased substantially during normal operation and does not materiallyincrease the force on the bellows. In this way, the possibility ofdeforming the bellows is minimized. With the spring 39 between thefulcrum 19 and the bellows, the fulcrum, although movable, remains inplace during normal operation.

I claim as my invention:

1. A condition responsive switch comprising a support, a member movablymounted on said support to move in response to changes in the conditionbeing sensed and having a forwardly projecting part formed with anaperture therein, an elongated spring anchored to said member with itsfree end projecting through said aperture, said spring urging said endagainst the outer edge of said aperture with a force of predeterminedmagnitude, an over center switch stationarily mounted on said support inthe path of said end and having a movable contact and a spring biasingthe contact toward one side of center, said switch requiring a forcegreater than said first force tc move said contact across center againstthe action of said spring and a force lesser than said first force tohold the contact in the over center position, an actuator for movingsaid contact across center and engaged by said free end, said elongatedspring yielding and said end moving away from the outer edge of saidaperture as said member moves toward said switch, and a stop spacedbehind said outer edge to limit the yielding movement of said free endand adjustably supported on said member to be spaced different distancesbehind the edge thereby to vary the range of movement of said end.

2. A condition responsive switch comprising a support, an over centerswitch stationarily mounted on said support and having a movable contactand a spring biasing the contact toward one side of center, said switchrequiring a first predetermined force to move said contact across centeragainst the action of said spring and a second and lesser force to holdthe contact in the over center position, an actuator for moving saidcontact across center, a member mounted on said support for,

able with said actuator, a second spring resiliently supporting saidelement on said member to yield and move relative to the member whenthe'element engages said actuator and the member moves toward theactuator, and spaced abutments on said member disposed on opposite sidesof said element to limit movement of the same relative to the member inbothdirections, said abutments being selectively movable relative toeach other to vary the range of movement of said element, said secondspring exerting a force of a magnitude between said first and secondforces whereby said contact is moved across center in both directionsafter said element engages one or the other of said abutments.

3. A condition responsiveswitch having, in combination, a support, firstand second members mounted on said support for movement relative to eachother, means responsive to thecondition to be sensed and operable tomove said members relative to each other according to the changes incondition, an over center switch mounted on said first member and havinga movable contact and a spring biasing the contact toward one side ofcenter, said switch requiring a firstpredetermined force to move saidcontact across center against the action of said spring and a second andlesser force to hold the contact in the over center position, anactuator for moving said contact across center, first and secondabutments rigid with said second member and spaced apart with the firstabutment near said actuator, an actuating element mounted on said secondmember to engage said actuator and supported for movement back and forthbetween a position against said first abutment and a position againstsaid second abutment, means for selectively moving one of said abutmentsrelative to the other to adjust the range of movement of said element,and a spring yieldably urging said element against said first abutmentwith a force of a magnitude between said first and second forces wherebysaid element moves against said second abutment before said contactmoves across center and the contact remains over center until theelement is engaged by said first abutment.

4. A condition responsive switch comprising a support, amember movablymounted on said support to move in response to changes in the conditionbeing sensed and having a forwardly projecting part formed with anaperture therein, an elongated spring anchored to said member with itsfree end projecting through said aperture, said spring urging said endagainst the outer edge of said aperture with a force of predeterminedmagnitude, an over center switch stationarily mounted on said support inthe path of said end and having a movable contact and a spring biasingthe contact toward one side of center, said switch requiring a forcegreater than said first force to move said contact across center againstthe action of said spring and a force lesser than said first force tohold the contact in the over center position, an actuator for movingsaid contact across center and engaged by said free end, said elongatedspring yielding and said end moving away from the outer edge of saidaperture as said member moves toward said switch, and a stop spacedbehind said outer edge and limiting the yielding movement of said freeend.

5. A condition responsive switch comprising a support, an over centerswitch stationarily mounted on said support and having a movable contactand a spring biasing the contact toward one side of center, said switchrequiring a first predetermined force to move said contact across centeragainst the action of said spring and a second and lesser force to holdthe contact in the over center position, an actuator for moving saidcontact across center, a member mounted on said support for movementtoward and away from said actuator in response to changes in thecondition being sensed, an actuating element carried by said member andengageable with said actuator, a second spring resiliently supportingsaid element on said member to yield and move relative to the memberwhen the element engages said actuator and the member moves toward theactuator, and spaced abutments on said member disposed on opposite sidesof said element to limit movement of the same relative to the member inboth directions, said second spring exerting a force of a magnitudebetween said first and second forces whereby said contact is movedacross center in both directions after said element engages one or theother of said abutments.

6. A condition responsive switch having, in combination, a support,first and second members mounted on said support for movement relativeto each other, means responsive to the conditions to be sensed andoperable to move said members relative to each other according to thechanges in condition, an over center switch mounted on said first memberand having a movable contact and a spring biasing the contact toward oneside of center, said switch requiring a first predetermined force tomove said contact across center against the action of said spring and asecond and lesser force to hold the contact in the over center position,an actuator for moving said contact across center, first and secondabutments rigid with said second member and spaced apart with the firstabutment near said actuator, an actuating element mounted on said secondmember to engage said actuator and supported for movementback and forthbetween a position against said first abutment and a position againstsaid second abutment, and a spring yieldably urging said element againstsaid first abutment with a force of a magnitude between said first andsecond forces whereby said element moves against said second abutmentbefore said contact moves across center and the contact remains overcenter until the element is engaged by said first abutment.

7. A condition responsive switch apparatus comprising a support, amember mounted on said support to move back and forth along aPIBClElfil'llllI'lfidPflfil, .a lever fulcrumed on said member, a switchmounted on said support and having an actuator engageable with a part onsaid lever whereby swinging of the lever about its fulcrum actuates theswitch, a bellows operable to expand and contract in response to changesin the condition to be sensed and having a part abutting against saidlever to swing the same in one direction, an abutment on said supportengaging said member to limit the movement of the member inone'direction, and a spring acting on said lever to hold the leveragainst said bellows part and simultaneously biasing said member againstsaid abutment to hold said fulcrum yieldably in a normal position, saidspring acting on said lever between said fulcrum and said bellows partand near the latter to prevent movement of the fulcrum when in saidnormal position and to permit yielding of said fulcrum withoutsubstantially increasing the pressure on said bellows.

8. A condition responsive switch apparatus having, in combination, asupport, a member mounted on said support to move relative to the sameback and forth along a predetermined path, an abutment disposed in saidpath and operable to engage a part on said member to limit movement ofthe member in one direction, a lever fulcrumed on said member andcarrying an actuating element, a switch mounted on said support andhaving an actuator engaged by said element whereby the switch isactuated upon swinging of said lever, means responsive to changes in thecondition to be sensed to turn said lever about its fulcrum, and aspring acting on said lever to urge the same toward said switch andsimultaneously biasing said part against said abutment to hold saidfulcrum yieldably in a normal position.

9. A condition responsive switch apparatus comprising a support, amember mounted on said support to move back and forth along apredetermined path, a lever fulcrumed on said member, a switch mountedon said support and having an actuator engageable with a part on saidlever whereby swinging of the lever about its fulcrum actuates theswitch, a bellows operable to expand and contract in response to changesin the condition to be sensed and having a part abutting against saidlever to swing the same in one direction, an abutment on said supportengaging said member to limit the movement of the member in onedirection, and a spring acting on said lever to hold the lever againstsaid bellows part and simultaneously biasing said member against saidabutment to hold said fulcrum yieldably in a normal position, saidspring acting on said lever near said bellows part to permit yielding ofsaid fulcrum without substantially increasing the pressure on saidbellows.

10. A condition responsive switch apparatus comprising a support havingan elongated guideway, a member having a part projecting into saidguideway to permit the member to move back and forth along a pathparalleling the guideway, a lever fulcrumed on said member and carryingan actuating element, a switch mounted on said support and having anactuator engaging said element to actuate the switch upon swinging ofsaid lever, means responsive to the condition to be sensed and operableto turn said lever about its fulcrum, an abutment engaged by said memberand limiting the movement of the member in one direction, and a springbiasing said member against said abutment to hold said fulcrum in anormal position but permitting the fulcrum to yield.

11. A condition responsive switch apparatus having, in combination, asupport, a member mounted on said support to move relative to the sameback and forth along a predetermined path, an abutment disposed in saidpath and operable to engage a part on said member to limit movement ofthe member in one direction, a lever fulcrumed on said member andcarrying an actuating element, a switch mounted on said support andhaving an actuator engaged by said element whereby the switch isactuated upon swinging of said lever, means responsive to changes in thecondition to be sensed to turn said lever about its fulcrum, and aspring biasing said part against said abutment to hold said fulcrum in anormal position but permitting the fulcrum to yield.

127 A condition responsive switch apparatus having, in combination, asupport, a member mounted on said support to move relative to the sameback and forth along a predetermined path, an abutment disposed in saidpath and operable to engage a part on said member to limit movement ofthe member in one direction, a lever fulcrumed on said member andcarrying an actuating element, a switch mounted on said support andhaving an actuator'cngaged by said element whereby the switch isactuated upon swinging of said lever, means responsive to changes in thecondition to be sensed to turn said lever about its fulcrum, a springbiasing said part against said abutment to hold said fulcrum in a normalposition but permitting the fulcrum to yield, and means selectivelyoperable to move said abutment relative to said part to change thenormal position of said fulcrum and thereby change the effective pointof operation of said switch.

13. A condition responsive switch apparatus comprising a support, alever fulcrumed on said support and carrying an actuating element, aswitch mounted on said support and having a movable contact and a springurging said contact in one direction, an actuator engaged by said leverand operable upon swinging of the lever to move said contact against theaction of said spring, a resilient bellows responsive to the conditionto be sensed and having a part abutting said lever, a spring actingbetween said support and said bellows and operable to load the bellows,and a separate spring acting on said lever and operating to hold thelever in engagement with said part as the lever is turned by the partupon expansion and contraction of said bellows.

14. In a condition responsive switch, the combination of, a support, anovercenter switch mounted on said support and having a movable contactand a spring biasing the contact toward one side of center, said switchhaving an actuator for moving said contact across center requiring afirst predetermined force to move the contact across center against theaction of said spring and a second and lesser force to hold the contactin the overcenter position, an elongated lever fulcrumed on said supportfor movement toward and away from said actuator and having two abutmentsthereon facing toward each other and spaced apart transversely of thelever and longitudinally of the direction of movement thereof toward andaway from the actuator, and an elongated spring anchored to andextending longitudinally of said lever with one end portion projectingand movable back and forth between said abutments and engageable withsaid actuator, said spring being flexed laterally of its length to urgesaid end portion against the one of said abutments nearest said actuatorwith a force intermediate said first and second forces.

References Cited in the file of this patent UNITED STATES PATENTS2,092,085 Riley Sept. 7, 1937 2,150,203 Bondurant Mar. 14, 19392,314,211 Hausler Mar. 16, 1943 2,691,084 Miller Oct. 5, 1954

